Recent change in how get_user() handles pointers [1] has a specific case for LAM. It assigns a different bitmask that's later used to check whether a pointer comes from userland in get_user().

While currently commented out (until LASS [2] is merged into the kernel) it's worth making changes to the LAM selftest ahead of time.

Add test case to LAM that utilizes a ioctl (FIOASYNC) syscall which uses get_user() in its implementation. Execute the syscall with differently tagged pointers to verify that valid user pointers are passing through and invalid kernel/non-canonical pointers are not.

Code was tested on a Sierra Forest Xeon machine that's LAM capable. The test was ran without issues with both the LAM lines from [1] untouched and commented out. The test was also ran without issues with LAM_SUP both enabled and disabled.

4/5 level pagetables code paths were also successfully tested in Simics on a 5-level capable machine.

[1] https://lore.kernel.org/all/20241024013214.129639-1-torvalds@linux-foundatio... [2] https://lore.kernel.org/all/20240710160655.3402786-1-alexander.shishkin@linu...

Signed-off-by: Maciej Wieczor-Retman maciej.wieczor-retman@intel.com --- Changelog v2: - Use mmap with HIGH_ADDR to check if we're in 5 or 4 level pagetables.

tools/testing/selftests/x86/lam.c | 89 +++++++++++++++++++++++++++++++ 1 file changed, 89 insertions(+)

diff --git a/tools/testing/selftests/x86/lam.c b/tools/testing/selftests/x86/lam.c index 0ea4f6813930..5818c075e1cd 100644 --- a/tools/testing/selftests/x86/lam.c +++ b/tools/testing/selftests/x86/lam.c @@ -4,6 +4,7 @@ #include <stdlib.h> #include <string.h> #include <sys/syscall.h> +#include <sys/ioctl.h> #include <time.h> #include <signal.h> #include <setjmp.h> @@ -43,7 +44,15 @@ #define FUNC_INHERITE 0x20 #define FUNC_PASID 0x40

+/* get_user() pointer test cases */ +#define GET_USER_USER 0 +#define GET_USER_KERNEL_TOP 1 +#define GET_USER_KERNEL_BOT 2 +#define GET_USER_KERNEL 3 + #define TEST_MASK 0x7f +#define L5_SIGN_EXT_MASK (0xFFUL << 56) +#define L4_SIGN_EXT_MASK (0x1FFFFUL << 47)

#define LOW_ADDR (0x1UL << 30) #define HIGH_ADDR (0x3UL << 48) @@ -370,6 +379,59 @@ static int handle_syscall(struct testcases *test) return ret; }

+static int get_user_syscall(struct testcases *test) +{ + int ptr_value = 0; + int ret = 0; + int fd; + void *p, *ptr = &ptr_value; + + p = mmap((void *)HIGH_ADDR, 1, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0); + + uint64_t bitmask = (p == MAP_FAILED) ? L4_SIGN_EXT_MASK : + L5_SIGN_EXT_MASK; + + munmap(p, 1); + + if (test->lam != 0) + if (set_lam(test->lam) != 0) + return 2; + + fd = memfd_create("lam_ioctl", 0); + if (fd == -1) + exit(EXIT_FAILURE); + + switch (test->later) { + case GET_USER_USER: + /* Control group - properly tagger user pointer */ + ptr = (void *)set_metadata((uint64_t)ptr, test->lam); + break; + case GET_USER_KERNEL_TOP: + /* Kernel address with top bit cleared */ + bitmask &= (bitmask >> 1); + ptr = (void *)((uint64_t)ptr | bitmask); + break; + case GET_USER_KERNEL_BOT: + /* Kernel address with bottom sign-extension bit cleared */ + bitmask &= (bitmask << 1); + ptr = (void *)((uint64_t)ptr | bitmask); + break; + case GET_USER_KERNEL: + /* Try to pass a kernel address */ + ptr = (void *)((uint64_t)ptr | bitmask); + break; + default: + printf("Invalid test case value passed!\n"); + break; + } + + if (ioctl(fd, FIOASYNC, ptr) != 0) + ret = 1; + + return ret; +} + int sys_uring_setup(unsigned int entries, struct io_uring_params *p) { return (int)syscall(__NR_io_uring_setup, entries, p); @@ -883,6 +945,33 @@ static struct testcases syscall_cases[] = { .test_func = handle_syscall, .msg = "SYSCALL:[Negative] Disable LAM. Dereferencing pointer with metadata.\n", }, + { + .later = GET_USER_USER, + .lam = LAM_U57_BITS, + .test_func = get_user_syscall, + .msg = "GET_USER: get_user() and pass a properly tagged user pointer.\n", + }, + { + .later = GET_USER_KERNEL_TOP, + .expected = 1, + .lam = LAM_U57_BITS, + .test_func = get_user_syscall, + .msg = "GET_USER:[Negative] get_user() with a kernel pointer and the top bit cleared.\n", + }, + { + .later = GET_USER_KERNEL_BOT, + .expected = 1, + .lam = LAM_U57_BITS, + .test_func = get_user_syscall, + .msg = "GET_USER:[Negative] get_user() with a kernel pointer and the bottom sign-extension bit cleared.\n", + }, + { + .later = GET_USER_KERNEL, + .expected = 1, + .lam = LAM_U57_BITS, + .test_func = get_user_syscall, + .msg = "GET_USER:[Negative] get_user() and pass a kernel pointer.\n", + }, };

static struct testcases mmap_cases[] = {